Recently, thin film made of a precious metal such as ruthenium or iridium has frequently been used in a thin-film electrode formed on a wafer of a semiconductor device.
Such thin film is most commonly produced through sputtering, which is a physical vapor deposition method. When thin film is produced through sputtering, the characteristics of the formed thin film vary considerably with the characteristics of a sputtering target material, such as purity and microstructure.
Thus, characteristics, such as specific resistance, which are required of a thin-film electrode in practice can be determined simply through control of the purity of a sputtering target material. In this connection, conventionally employed sputtering target materials which have been produced through casting or powder metallurgy have yielded reasonably satisfactory characteristics.
However, during use of a sputtering target produced through casting or powder metallurgy, a minute cluster mass tends to be chipped from the sputtering target and adhere on the formed thin film surface, to thereby cause, for example, a change in electrical resistance, which is detrimental to product quality and results in a reduction in product yield.
Meanwhile, when a sputtering target material is produced through powder metallurgy, the target material is typically hot-shaped under hydrostatic pressure through an HIP method. Particularly, intergranular voids may remain in the thus-produced sputtering target material, and gas may be trapped in the voids. Once the trapped gas is released, the gas affects the stability of vacuum which is required during sputtering, and may deteriorate film characteristics.
In addition, if such a sputtering target material having gas-trapping voids is heated during sputtering, the gas remaining in the sputtering target material expands by heat, to thereby possibly cause damage to the sputtering target per se, in forms such as blow-holes.